Electrical control apparatus



g- 19, 1930' R. MACLAREN 1,773,234

ELECTRICAL CONTROL APPARATUS Filed Dec. 1926 Patented Aug. 19, 1930 PATENT QFFECE ROBERT MACLAR-EN, OF CULROSS, SCOTLAND ELECTRICAL GUHTRGL APLPAB-ATUS Application filed December 9, 1926, Serial No. 153,?12, and in Great Britain December 31, 1925.

My invention relates to improvements in and connected with electrical control apparatus, and has for its object the automatic cutting off and on of the electrical supply in furnaces, ovens and the like.

In carr ing out this invention, I provide an expansion bulb filled with a medium which operates a parabolic shaped steel diaphragm carrying a fined silver point which under heat comes in contact with an adjustable silver pointmounted on a secondary piston, the se i: in turn being mounted on a primary on. The primary piston is moved out and in by mom 5 oil: a thumb-screw having a pointer over a graduated dial. This, it will be observed, alters the position, of one silver point relatively to the other silver point and so raises the temperature control point. The control is so arranged that, when the medium expands under heat, the circuit is closed, thus operating a relay and so the main circuit of an electric furnace or the like.

In order that my invention may be properlv understood and readily carried into e1?- i'bct, I have hereunto appended one sheet of drawing, which is a sectional elevation illustratii a my invention.

' rring to the drawing, A and B are the two silver points, A being suitably connected to th steel parabolic diaphragm C. A second diaphragm C is used to seal up the liquid expansion medium in the container E which suitably connected to the main body D. The container E is inserted into the apparatus the heat of which requires to be controlled. The silver poin A together with a plate mounting is suitably insulated from the steel diaphragm O with its plate by the insertion of a sheet F of mica or other suitable material. The other silver point B is mounted on a secondary piston G carried on a disc H and is free to slide through the center hole on the disc H, a small spring I being provided between the flange of the secondary piston G and the disc H to cause the silver point to return to its original position when the temperature falls The disc H is suitably connected at its upper end to the primary piston J, which is contained in an extension D 01": the main body D, the lower end oi? the primary piston J being contained in the cap-nut K which capnu't K is screwed on the extension D of the -main body I). A spring L, is provided, one end bearing against the extension D, the other bearing against a flange J fixed to the lower end of the piston J The object of the spring L is to keep the primary piston in contact with the adj usting screw K of the cap-nut K. M is the handle of the cap-nut -for operating the primary piston J and in turn the silver point B.

Under heat the contents of the container E expand, this causes the parabolic diaphragms C and to move forward, conse quently carrying the point A up to the point- B, thus forming an electrical connection, and used to operate a suitable switch.

Claim:

Electrical control apparatus compri ng a container for an expansive medium, a diapl'iragm arranged for movement by the expansion of the ex ansive medium, a contact pointcarried by said diaohragm, body having a bore opposite said contact point, a primary piston arranged for movement in said bore, a disc on the end of said piston op posed to said contact point, said having a bore, a secondary piston movable in the bore of said disc, a contact point on said ondary piston, opposed to the first named contact point, a spring a Live to move the secondary piston with contact point toward the first named contact point, a spring active to move the prime. ry piston in the reverse direction to that of the secondary piston, a cap-nutenclosing primary piston and the last named spring and means to adjustably move the primary piston and. hence also the secondary piston against the tension of: the second named spring.

In witness whereof? I atria my signature.

ROBERT rnrcLAi-nas. 

